1. Field of the Invention
This invention relates to tractors and, more particularly, to a transmission apparatus of a tractor having a mid-mount type lawn mower.
2. Description of the Related Art
Examples of tractors having a mid-PTO shaft for allowing a mower to be disposed under a tractor body between front and rear wheels are disclosed in Japanese Patent Laying-Open Publication H8-282312 and Patent Laying-Open Publication H7-232567. In these tractors, an engine mounted on a front portion of the tractor body and a transmission disposed in a rearward position of the tractor body are interlocked through a drive shaft. Such a construction secures a space for accommodating the mower. That is, a sufficient space is secured for vertically movably accommodating the mower by arranging the engine and transmission in forward and rearward positions of the tractor body. The mower may be raised to a sufficient height above the ground when the tractor makes a non-operational run.
The size of a tractor is determined largely by the wheelbase which is the distance between front and rear wheels. Tractors of small overall size are desired particularly for use on small farms and for personal use. It is thus desirable to reduce the wheelbase to realize a small tractor capable of accommodating a working implement such as a mower in an intermediate position thereof.
However, when the wheelbase is reduced, it is difficult to secure a sufficient space for a working implement such as a mower since the transmission of the tractor occupies a large space.
An object of this invention is to provide a small tractor, which secures a sufficient space for a mower.
The above object is fulfilled, according to this invention, by a tractor comprising a pair of frames extending in a fore and aft direction of the tractor and spaced from each other transversely thereof, an engine disposed in a forward region of the pair of frames, a transmission case extending and supported between rear portion of the pair of frames, a rear wheel differential housed in the transmission case, a pair of rear wheel axles connected to a pair of rear wheels of the tractor and having an axis extending transversely of the rear wheel differential, a power take-off clutch disposed above the rear wheel differential, and a change speed gearing mechanism disposed between the front surface of the transmission case and a virtual plane extending vertically through the axis.
In the above construction, the rear wheel differential and the PTO clutch are arranged vertically. The change speed gear mechanism has a flat configuration thin in the fore and aft direction, which is disposed between the front surface of the transmission case and a virtual plane extending vertically through the axis of the rear wheel axles. This construction provides a reduced fore and aft length between the front surface of the transmission case and the rear wheel axles, compared with a construction in which the PTO clutch is disposed forwardly of the differential or the change speed gear mechanism is disposed forwardly of the differential.
Thus, the tractor according to this invention realizes a reduced wheelbase without reducing the diameters of front and rear wheels or the fore and aft length of a working implement. The above construction enables the tractor to be built compact while securing a sufficient space for the working implement disposed in the lower position thereof.
In an embodiment of this invention, the front cover of the transmission case, preferably, has an oil filter disposed on a lower portion thereof, and supply and drain oil passages which are through holes formed in the front cover to extend parallel to the front surface. With this construction, the required supply and drain oil passages may have a reduced length or no length to achieve a reduction in weight. Such oil passages are less vulnerable to damage through contact with other objects than where supply and drain oil passages are in the form of pipes, hoses or the like arranged along an outer surface of the transmission case.
In a further embodiment of this invention, the tractor includes front wheels, rear wheels, a transmission case, a rear axle, and a framework. The transmission case is disposed adjacent to the rear wheels. The transmission case has right and left walls, a front wall, and a rear wall. The rear axle is supported by the transmission case. The framework substantially forms a body of the tractor and extends in a fore and aft direction of the tractor. The framework includes a first frame and a second frame. The first frame has its rearward end region connected to the left wall of the transmission case. The second frame has its rearward end region connected to the right wall of the transmission case. The tractor further includes a rollover protection structure (ROPS) supported by the framework.
The ROPS may include-right and left legs extending upwardly, and a cross portion connecting the right and left legs. The left leg may be supported by the first frame through a left post, and the right may be supported by the second frame through a right post. The right and left connecting regions between the framework and the transmission case may be located adjacent to right and left connecting regions between the framework and the respective right and left posts, respectively. The tractor may further include horizontal right and left mounting seats that are provided at one side of the respective right and left posts. The mounting seats may have the right and left legs of the ROPS connected thereto, respectively. The mounting seats and the right and left legs of the ROPS may be connected to each other with right and left fenders interposed therebetween, respectively.
Other features and advantages of this invention will be apparent from the following description of the preferred embodiment to be taken with reference to the drawings.